Von Willebrand factor (vWf) protein is synthesized in endothelial cells and megakaryocytes. We identified differences in the carbohydrate content between plasma and platelet vWf. Studies are now in progress to specify the role(s) of carbohydrates in vWf function, survival, molecular size, and bioactivity. 0-linked carbohydrates appear to be important in ristocetin-medicated binding. Plasma vWf binds more with ristocetin than platelet vWf. We plan to further study the differences in carbohydrate content of the two proteins.